-- Sydney heading very. Rapidly developing situation worse than I had been briefed. Throughout the night I think you know the basics that. So that's best landing news he's dead -- spent two years on the run we have. And MBTA. Officer was seriously wounded and -- your dream right now we have and MIT. Security. Zero. We didn't kill. -- -- -- massive manhunt under way. Lot the law enforcement involved in that. Into the system that -- -- suspended all service on the MBTA. Public transit. Service that will continue until. It's safe -- and always on Monday. We're asking people to sheltered in place in other words to stay indoors. With the doors locked and not to open the door for anyone other than -- apparently identified law enforcement officer and that applies. Here in Watertown where we are right now but also Cambridge. Waltham. Newton Belmont. And it just like all of Boston's Paul plus. This is -- this is a serious situation we're taking it seriously we're asking the public. To take it seriously as well and assist law enforcement by following those simple construction. We get every asset. That we can possibly Muster. And media on the ground right now. They are doing a terrific job -- working. In concert with each other that we -- going to need to -- to help must help them stay safe. Thank you don't know is don't assume this is -- rapidly developing situation. And Alaska gold received information. But I communicated to Mayor Menino Mayor Menino -- just -- come here. Did you tell you. The shoulder employees. -- recommendation. Has been extended through the city of Boston. There's a lot of information coming in working very closely with federal authorities in Washington. We are assuming all -- -- -- Paul. Potential. Leaves -- there are offices are -- bureau a city right now. -- please be patient with us -- -- us if you see anything suspicious. Let us know. We are trying to make a decision as early as possible that this is an ongoing situation or -- This is an ongoing. Situation. The girls and -- the island. For someone -- -- saying thank you so each and every one of you you've gotten the message out there into the neighborhood I have to ask you to continue to do that. Our number one priority right now is -- these neighborhoods here in Watertown and making them safe in finding this individual. That's -- we're committed to we need more time we're making significant progress up there. But it may take hours to do this so please bear with us I know that there are a lot of questions -- we'll have plenty of time to address those and after this. But for right now this is about public safety this is about the Watertown neighborhood so please give us. That -- which will be back shortly thank you thank you. Law enforcement officials in Massachusetts right there -- an urgent alert they are asking everyone. Everyone in the city of Boston and -- surrounding suburbs to say inside right now it is an ongoing situation of fast developing situation. According to police commissioner Ed Davis some here would Dan Abrams our GMA legal analyst what an extraordinary move right now the entire town asking everyone. In the city of Boston to stands. -- imagine a major American city. Now being told that everyone should stay inside -- shows you how seriously they're taking this this is not just about. A criminal suspect. This is about someone who is a danger. To the entire community. And again the questions that still need to be answered are so voluminous including. Are there others out there who he's connected to. And I think that's as much of a concern is anything. Yes they want to catch this -- yes they want to stop him. But they know who he hits it's the unknowns that I think for law enforcement here which are are even more -- and I wanted to Pierre Thomas on that we just heard the police commissioners -- Appear that they they called Mayor Menino of this request that everyone stay inside because the information came in just the last half hour. George extraordinary situation. They are confirming what we were telling our viewers a little while ago that they don't -- yet know whether this man and his. Potential brother has support. Does he have support right now. Part of the investigation is -- and looking at all of his associates. Who knows this man could there be other people out -- so the threat is not just to the suspect number two. Into the what he might do and we've seen what they're capable of this morning the concern is. Do they have support. That's the unknown until they know that they're asking an entire city. I can't think of anything like this since 9/11 to set down stay inside don't go outside as what police are telling people. Never heard anything like before let's go to Brian Ross on the ground in Watertown right now thousands of police. Converging on that small town near the surrounding suburbs of Boston. And George I would say not since September 11 of 2000. One has -- -- a sense of powerlessness by the people who live in America that they are at the mercy of unknown terrorists. Have been asked in Boston to stay inside and lock their doors not go out. It's an astounding situation. We haven't really seen in twelve years. And Brian we knew we just heard -- tells a few moments ago about one of the killers -- that the suspect now dead just walking cooling. Towards pleas to the police had any idea in which direction. The the suspect number two -- when he was in that Mercedes SUV. They thought he took off they thought they had -- surrounded in in. Hear about. And reports since then on spotting him elsewhere physically and we're just about. And -- around him. And we're about the another announcement here let's go to. You have to have always Nolan and the -- is at least I'm getting refueled and his office Wednesday evening news audience how. Six point -- NAC. MI LL AM he will not be taking any questions -- restatement and O'Neill chief. Good morning I just wanted to release the names of the officer you. It was -- early it's name is Richard H Donahue Julia. -- -- -- -- -- -- -- He's 33 years of age and he's been a transit police officer for three years he's currently at mount Auburn hospital thank you. It's anything other little -- really thank -- got so. This this adds of course said George -- we had great concerns I'm. These are we're all men are -- -- not afraid to kill children who kill law enforcement officers. -- support -- received the messages going out that no one really is is safe as long as. This man and perhaps his associates are on the street so again is a sense of fear that pervades here real tensions in the -- with the police thousands of them still unable to find this one man and. In all 625000. Residents the city of Boston has to stay inside right now several million. In the surrounding suburbs and -- stay on top of this all day long and ABC news and we return now to Good Morning America.

This transcript has been automatically generated and may not be 100% accurate.

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{"id":18996422,"title":"Boston Marathon Bombing: 'Suspect 2 Is on the Run'","duration":"7:43","description":"Officials say that one suspect has been killed while another is loose in Massachusetts.","url":"/GMA/video/boston-marathon-bombing-suspect-on-the-run-18996422","section":"GMA","mediaType":"default"}